1. Field of the Invention
Exemplary aspects of the present invention generally relate to an image forming apparatus such as a printer, a facsimile machine, and a copier.
2. Description of the Background Art
Related-art image forming apparatuses, such as copiers, printers, facsimile machines, and multifunction devices having two or more of copying, printing, and facsimile functions, typically form a toner image on a recording medium (e.g., a sheet of paper, etc.) according to image data using an electrophotographic method. In such a method, for example, a charger charges a surface of an image carrier (e.g., a photoconductor); an irradiating device emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; a developing device develops the electrostatic latent image with a developer (e.g., toner) to form a toner image on the photoconductor; a transfer device transfers the toner image formed on the photoconductor onto a sheet of recording media; and a fixing device applies heat and pressure to the sheet bearing the toner image to fix the toner image onto the sheet. The sheet bearing the fixed toner image is then discharged from the image forming apparatus.
Image forming apparatuses often use a process cartridge detachably installable in the image forming apparatuses. The process cartridge includes the photoconductor and at least one of the charger, the developing device, the cleaning device, and other process units provided around the photoconductor within a casing thereof. A main reference portion and a sub-reference portion are generally provided to the process cartridge for positioning the process cartridge relative to the body of the image forming apparatus. When the process cartridge is inserted into the image forming apparatus in an X-axis direction, the main reference portion positions the process cartridge relative to the body of the image forming apparatus in Y-axis and Z-axis directions, both of which are perpendicular to the X-axis direction. The sub-reference portion positions the process cartridge relative to the body of the image forming apparatus around the X axis. An insertion hole serving as a main reference portion receiver into which the main reference portion is inserted and a slot serving as a sub-reference portion receiver into which the sub-reference portion is inserted are formed in the body of the image forming apparatus. The slot extends parallel to a line connecting the center of the main reference portion with the center of the sub-reference portion along the X axis. The main reference portion is inserted into the insertion hole to position the process cartridge relative to the body of the image forming apparatus in both the Y-axis and Z-axis directions. The sub-reference portion is inserted into the slot to position the process cartridge relative to the body of the image forming apparatus around the X axis.
In a case in which the main reference portion is inserted loosely into the insertion hole due to manufacturing tolerance or the like, a load exerted during operation moves the main reference portion within the insertion hole, possibly resulting irregular images including banding and so forth. In addition, in a full-color image forming apparatus in which multiple process cartridges for each color are installed therein, loose installation of the process cartridges may cause color shift in output images.
To counteract the effect of the operating load, the image forming apparatus can be given a pressing unit that presses the main reference portion inserted into the insertion hole against one side of the insertion hole to keep it stationary. Accordingly, the main reference portion is prevented from moving within the insertion hole even when it is inserted into the insertion hole with looseness. As a result, the process cartridge is accurately positioned relative to the body of the image forming apparatus in both the Y-axis and Z-axis directions.
However, in such an arrangement the process cartridge shakes against the body of the image forming apparatus around the X axis when the sub-reference portion is short relative to the width of the slot due to manufacturing tolerance. Consequently, the operating load moves the process cartridge around the X axis, possibly resulting in irregular images including banding and so forth. It is conceivable that a second pressing unit that presses the sub-reference portion toward a lateral direction of the slot is further provided to the image forming apparatus to prevent movement of the process cartridge around the X axis. However, provision of the second pressing unit increases number of components and production costs.